"We cannot be a party that nominates someone who refuses to
condemn white supremacists and the Ku Klux Klan," Rubio said
Sunday.

For his part, Trump said that he did not disavow Duke's
endorsement during a Sunday CNN interview because he was
provided with a "bad earpiece" that made it
difficult to hear. He also noted that he disavowed Duke's
endorsement at a Friday press conference during which he rolled
out the endorsement of New Jersey Gov. Chris Christie.

"I was sitting in a house in Florida, with a bad earpiece,"
Trump told NBC's "Today" show Monday. "I could hardly hear
what he's saying. I hear various groups. I don't mind disavowing
anyone. I disavowed Duke the day before at a major conference."

Trump and Romney have been increasingly critical of each other in
public. Despite Trump's repeated refusals, Romney has pushed the former reality-television star
to release his tax returns, alleging a possible "bombshell"
contained within them.

"Mitt Romney, who totally blew an election that should have been
won and whose tax returns made him look like a fool, is now
playing tough guy," Trump fired back in a tweet last week.